export function commonChars(a: string, b: string): number {
  if (a.length === 0 || b.length === 0) {
    return 0;
  }

  const newA = new Set(a.toLowerCase());
  const newB = new Set(b.toLowerCase());

  let count = 0;
  for( const characterA of newA) {
    if(newB.has(characterA)) {
      count++
    }
  }
  return count;
}